Physics and Physicists

Friday, February 16, 2018

They seem to be making a steady and impressive success along this line.

A new paper in Science[1] has shown an impressive result of the possibility of causing 3 different photons to be "bound" or entangled with one another after traversing through a cold rubidium atom gas.

In controlled experiments, the researchers found that when they shone a
very weak laser beam through a dense cloud of ultracold rubidium atoms,
rather than exiting the cloud as single, randomly spaced photons, the
photons bound together in pairs or triplets, suggesting some kind of
interaction — in this case, attraction — taking place among them.

Now, without going overboard with the superlatives, it must be stressed that this does not occur in vacuum, i.e. 3 photons just don't say hi to one another and decide to hang out together. The presence of the cold rubidium gas is essential for a photon to bound with one of the atoms to form a polariton:

The researchers then developed a hypothesis to explain what might
have caused the photons to interact in the first place. Their model,
based on physical principles, puts forth the following scenario: As a
single photon moves through the cloud of rubidium atoms, it briefly
lands on a nearby atom before skipping to another atom, like a bee
flitting between flowers, until it reaches the other end.

If another photon is simultaneously traveling through the cloud, it
can also spend some time on a rubidium atom, forming a polariton — a
hybrid that is part photon, part atom. Then two polaritons can interact
with each other via their atomic component. At the edge of the cloud,
the atoms remain where they are, while the photons exit, still bound
together. The researchers found that this same phenomenon can occur with
three photons, forming an even stronger bond than the interactions
between two photons.

This has almost the same flavor as the "attraction" between two electrons in a superconductor to form the bound Cooper pairs, which requires a background of lattice ion vibration or virtual phonons to mediate the coupling.

So photons can talk to one another, and in this case, 3 of them can hang out together. They just need a matchmaker as an intermediary, since they are just way too shy to do it on their own.

And with that sugary concoction, I think I need more coffee this morning.

Unfortunately, there is a bit of misconception going on here. You are not actually seeing the single strontium atom, because it highly depends on what you mean by "seeing". The laser excites the single strontium atom, and then the strontium atom relaxes and releases energy in the form of light. This is the light that you are seeing, and it is probably a result of one or more atomic transition in the atom, but certainly not all of it.

So you're seeing light due to the atomic transition of the atom. You are not actually seeing the atom itself, as proclaimed by some website. This is the nasty obstacle that the general public has to wade through when reading something like this. We need to make it very clear when we report this to the media on what it really is in no uncertain terms, because they WILL try to sensationalize it as much as they can.

Tuesday, February 13, 2018

I mentioned earlier that the g-2 experiment at Fermilab was about to start (it has started now), which is basically a continuation and refinement of what was done several years ago at Brookhaven. In case the importance of this experiment escapes you, Don Lincoln of Fermilab has written a piece on the CNN website on this experiment and why it is being done.

If you are not in science, you need to keep in mind this important theme: scientists, and definitely physicists, like it A LOT when we see hints at something that somehow does not fit with our current understanding. We like it when we see discrepancies of our results with the things that we already know.

This may sound odd to many people, but it is true! This is because this is why many of us get into this field in the first place: to explore new and uncharted territories! Results that do not fit with our current understanding give hints at new physics, something beyond what we already know. This is exploration in the truest sense.

This is why there were people who actually were disappointed that we saw the Higgs, and within the energy range that the Standard Model predicted. It is why many, especially theorists working on Supersymmetry, are disappointed that the results out of the LHC so far are within what the Standard Model has predicted.

This is basically an inverse Compton scattering. The latest experiment that studies this has been getting a bit of a press, because of the sensationalistic claims of light "stopping" electrons in their tracks.

A review of the experiment, and the theory behind this, is sufficiently covered in APS Physics, and you do get free access to the actually paper itself in PRX. But after all the brouhaha, this is the conclusion we get:

The differing conclusions in these papers serve as a call to improve the
quantum theory for radiation reaction. But it must be emphasized that
the new data are too statistically weak to claim evidence of quantum
radiation reaction, let alone to decide that one existing model is
better than the others. Progress on both fronts will come from
collecting more collision events and attaining a more stable electron
bunch from laser-wakefield acceleration. Additional information could
come from pursuing complementary experimental approaches to observing
radiation reaction (for example, Ref. [7]), which may be possible with the next generation of high-intensity laser systems [8].
In the meantime, experiments like those from the Mangles and Zepf teams
are ushering in a new era in which the interaction between matter and
ultraintense laser light is being used to investigate fundamental
phenomena, some of which have never before been studied in the lab.

I know that they need very high-energy electron beam, but the laser wakefield technique that they used seem to be providing a larger spread in energy than what they can resolve:

Both experiments obtained only a small number of such successful events,
mainly because it was difficult to achieve a good spatiotemporal
overlap between the laser pulse and the electron bunch, each of which
has a duration of only a few tens of femtoseconds and is just a few
micrometers in width. A further complication was that the average energy
of the laser-wakefield-accelerated electrons fluctuated by an amount
comparable to the energy loss from radiation reaction.

I suppose this is the first step in trying to sort this out, and I have no doubt that there will be an improvement in such an experiment soon.

Tuesday, February 06, 2018

While this technique has become more common, and there are already several places here in the US that are researching this, this is a nice article to introduce to you the current state-of-the-art in using charged particles in medicine, especially in treating and attacking cancer. It appears that the use of carbon ions is definitely catching up in popularity over the current use of protons.

When you read this article, pay attention to the fact that this is an outcome of our understanding of particle accelerators, that this is a particle accelerator applications, and that high-energy physics experimental facilities are often the ones that either initiated the project, or are hosting it. So next time someone asks you the practical applications of particle accelerators or particle physics, point to this.

Wednesday, January 31, 2018

I took that title loosely from this article that reviews a new study on how various groups of people think. To be fair, the paper being cited actually debunks that myth that religious people are less intelligent than non-religious people.

However (you know that was coming, didn't you?), it points out that religious people tend to rely heavily on intuition when there is an apparent conflict between intuition and logic. In other words, the more religious a person is, the more likely he/she will abandon rational thinking and rely on his/her intuition.

This is actually consistent with an earlier study that I mention on here. In that study, it was discovered that non-scientists are more likely to ignore scientific facts and evidence in favor of a view that support their values. Flat-Earth believers, anyone?

The problem in all of this is that (i) logic and rational thinking are the best methodology that we know of to come up with a valid conclusion, (ii) facts and evidence are being ignored or dismissed, and (iii) our intuition has been known to be terribly wrong and unreliable.

In science, intuition can only go so far, and we often abandon our intuition once it has been trumped by facts and evidence. This is why science evolves and improves over time. So when someone goes against that, and lean more on faulty intuition than logic and rational thinking, we then are into no-rules and no-holes-barred territory. Is this why a lot of people still believe in irrational and uncorroborated ideas and opinions?

I don't know. To me, dealing with public opinions and why such-and-such group of people or individual thinks that way is more mysterious than any of the physics research that I've done. Human beings are irrational creatures by nature, I suppose.

Sunday, January 28, 2018

This is a common problem that many of us who teach intro physics encounter. Students, and the general public, often have a severe misunderstanding of the concept of "weightlessness", and equate that to having zero gravity. Certainly the example of being in a free-falling elevator, or even the example of the zero-g simulation in airplanes (the "vomit comet") are clear examples where one can be weightless but still in an environment with g not being zero.

It is one of those topics where, as physics instructors, we are resigned to a life-sentence of educating people non-stop about this misconception.

Friday, January 26, 2018

The old muon g-2 experiment that was at Brookhaven was taken apart, and rebuilt at Fermilab. Now, after the logistic challenge of moving the huge magnet from there, and after the long hard work of rebuilding the facility, the muon g-2 is now about ready to start its run.

The facility is now better than ever, and physicists are hoping that there will be an anomaly in the measurement, indicating new physics beyond the Standard Model.

In 2013, the g-2 team lugged the experiment on a 5000-kilometer odyssey from Brookhaven to Fermilab, taking the ring by barge around the U.S. eastern seaboard and up the Mississippi River.
Since then, they have made the magnetic field three times more uniform,
and at Fermilab, they can generate far purer muon beams. "It's really a
whole new experiment," says Lee Roberts, a g-2 physicist at Boston
University. "Everything is better."

Over 3 years, the team aims to collect 21 times more data than during
its time at Brookhaven, Roberts says. By next year, Hertzog says, the
team hopes to have enough data for a first result, which could push the
discrepancy above 5 σ.

Thursday, January 25, 2018

This would be funny if it wasn't so sad, and scary because these people presumably vote!

I read about this Flat Earth International Conference (honest!), and I can't believe the idiotic stuff that was written in the article. I'm going to ignore the paranoid claims about conspiracy and stuff. I'm not here to deal with their psychotic problems. However, I can deal with the science, and in particular, when idiots try to use physics to justify their stupidity.

Many flat-Earthers believe in testing the theory.

Darryle
Marble said he conducted his own in-flight experiment using a leveler
to test if the plane was flying parallel to a flat Earth.

"If
it were a sphere then the surface of the Earth still would have been
curving underneath the airplane while it's flying level," he reasoned.
"It’s so simple it'll go right over your head," he said adding that
people who have flown planes allegedly told him they "haven’t seen any
curvature."

First of all, they don't believe astronauts who have gone into space when they said that the earth is a sphere, but yet, they want to use human observation from airplane rides! This is an example of pick-and-choose.

Secondly, a leveler? Seriously?

Assuming that the plane is moving at a constant speed and at a constant altitude, this means that the plane is moving parallel to the earth's surface all the time. That's the definition of constant altitude. If the plane were to fly "straight with respect to the spatial coordinates", then it would be increasing in altitude! If that were to happen, the leveler will indicate several things (i) the acceleration due to the plan having to increase its altitude and (ii) gravity will act not straight down anymore. Any of these will affect the leveler.

But really, does the fact that if one head east continuously and end up at the same position later while in the plane, means nothing to these people?

There are many evidence that the earth is a sphere, and many of these are plain obvious. The fact that different parts of the earth having opposite seasons at a given time of the year is one clear example. A flat earth will not result in different parts of the earth having different daylight hours and different seasons.

But there is another clear test here that have been too obvious: using a Faucault pendulum. How would these idiots explain not only the change in the plane of oscillation of the Faucault pendulum over a period of 24 hrs, but also the fact that (i) the change in the plane of oscillation is in the OPPOSITE direction for those having the opposite season (i.e. northern hemisphere versus southern hemisphere) and (ii) there is no change in the plane of oscillation at the equator.

Of course, to understand the significance of this observation, one actually must know the physics involved in a Faucault pendulum, and the conservation of angular momentum. But hey, maybe physics and all these conservation laws are also more conspiracies.

Again, to paraphrase Kathy Griffin: "These people are proud of their aggressive ignorance."

OK, so it may be odd that I want to highlight a beginner's topic on a popular subject on a blog that has been around for years. But hey, I get new people following this thing all the time, and I often get the same questions on basic physics.

So here's a simple, basic intro video on Special Relativity. In fact, Don Lincoln will be producing a series of such videos on this topic for those of you who want to know about Special Relativity, but was too afraid to ask.

Tuesday, January 23, 2018

Clifford Johnson of USC has an interesting article on ways to introduce science (or physics in particular), back into things that the public usually gravitate to. In particular, he asks the question on how we can put legitimate science into popular culture so that the public will get to see it more regularly.

Science, though, gets portrayed as opposite to art, intuition and
mystery, as though knowing in detail how that flower works somehow
undermines its beauty. As a practicing physicist, I disagree. Science
can enhance our appreciation of the world around us. It should be part
of our general culture, accessible to all. Those “special talents”
required in order to engage with and even contribute to science are
present in all of us.

So how do we bring about a change? I think using the tools of the
general culture to integrate science with everything else in our lives
can be a big part of the solution.

Read the rest of the article on how to inject science into popular entertainment, etc.